What is Trump trying so hard to cover up?

It’s often said, in assessing recurrent Washington scandals, that the cover-up is worse than the crime.

That was certainly true when President Richard Nixon directed the CIA and the FBI to cover up the break-in by his campaign operatives of Democratic national headquarters in the Watergate building. The burglars went to jail, but it took two years for disclosure of Nixon’s role to cause his forced resignation.

Similarly, the primary focus of the current probe of possible collusion between the Russians and Donald Trump’s 2016 presidential campaign has been on potential charges of obstructing justice against Trump for actions that include firing FBI Director James Comey and helping to write a misleading memo about a campaign meeting with several Russians.

What’s been less evident is what explicit concerns are prompting Trump to block an investigation that he has labeled a “witch hunt,” designed to delegitimize his election.

The swirling controversy over the House GOP memo assailing top Justice Department and FBI officials didn’t shed any light on that.

After all, even if its allegations against FBI and Justice Department officials are true — and critics have shown they are at least misleading — Carter Page was just one of several Trump aides who had questionable associations with the Russians. And while some Republicans claim Christopher Steele’s flawed memo was a primary factor in approving the October 2016 decision to spy on Page, the memo specifies that another Trump campaign aide, George Papadopoulos, actually triggered the probe three months earlier.

Here are potential clues as to what in the probe might most concern Trump:

Trump has long sought to cultivate Russian ties. His interest goes back to the 1980s when he first visited Moscow to explore building a hotel there, and he also floated the idea of helping negotiate a deal to reduce U.S. and Soviet nuclear weapons. During the 2016 campaign, he repeatedly praised Vladimir Putin, saying when he grabbed part of Crimea that “the people of Crimea … would rather be with Russia” and calling the Russian president “a better leader” than President Barack Obama. At the 2016 Republican convention, Trump’s operatives watered down a platform plank representing the traditional GOP position pledging “lethal” U.S. support if Russia attacked Ukraine.

Given those factors, Trump’s suggestion that he would not be fully supportive of all NATO countries in the event of a Russian attack, and Putin’s dislike of Hillary Clinton for criticizing his conduct of the 2012 Russian presidential election, it was hardly surprising that the Russians favored Trump.

Trump’s people were actively engaged in soliciting help from the Russians. Trump himself publicly welcomed the Wikileaks material hacked from the Democratic National Committee and urged that it all be made public. His son Donald Jr. met in June 2016 with Russians promising dirt on Clinton, one of the central events that independent counsel Robert Mueller is investigating. Though Trump has repeatedly claimed that he has nothing to do with Russia, some aides and even some family members can’t make the same claim.

Carter Page, the central figure in the GOP memo, has longtime ties to the Russian energy giant Gazprom and is considered by some to have been a Russian spy. The lies to the FBI by Trump’s first national security adviser, Michael Flynn, stemmed from his apparent suggestion to the Russian ambassador that Trump might ease Obama-era sanctions against Russia. A key unanswered question: Did he act at Trump’s direction? That could create serious problems for the president.

There are significant non-campaign ties between Trump’s businesses and Russians. In 2008, Donald Jr. told a real estate conference: “Russians make up pretty disproportionate cross-section of a lot of our assets. We see money pouring in from Russia.” After he started running for president, Trump explored building a hotel in Moscow. Josh Marshall may have fingered the underlying fact when he concluded in Talking Points Memo last year that Trump has been “highly reliant on money from Russia to finance his debts.” Russians are believed to have helped finance many Trump projects around the world and are known to have purchased dozens of condos in Trump-owned buildings in what some consider a money-laundering operation.

Given this maze of connections between Trump, his family, his campaign officials and the Russians, the question is: Where is he afraid of disclosure? Fears that details of Russian election interference would somehow taint the results hardly seem like the real reason. Besides, Mueller has reportedly hired a large number of money laundering experts to examine Trump’s financial connections with the Russians.

So far, public discussion of Mueller’s probe continues to focus on Trump’s efforts to undercut or block it. Until we know more underlying details, his motivation will remain a mystery. But his actions make clear he wants to keep something hidden.